Surface

Under Edit there are three items. They are Surface Type, Set Current Surface, and Implicit Surface.

1. Surface Type allows a user to specify the surface type that will be used for creating the next surface. This system supports four types of surfaces:
   • Bézier Surface selects the surface to be a Bézier surface.
   • Rational Bézier Surface selects the surface to be a rational Bézier surface.
   • B-spline Surface selects the surface to be a B-spline surface.
   • NURBS Surface selects the surface to be a NURBS surface.

2. Set Current Surface lets a user to pick a surface to be the current surface. The IDs of all surfaces on the drawing canvas are listed. Thus, selecting a surface ID will make the corresponding surface the current one.

3. Implicit Surface is designed for processing implicit surfaces. It has the following three sub-items:
   • Define Implicit Surface activates the implicit surface subsystem. Once the implicit surface module is activated, you will see an editor window for you to type in the equation of an implicit surface. This subsystem will compile, run and display a polygonized version of the given implicit surface. See A Quick Tour for the details.
   • Unload Implicit Surface deactivates the implicit surface subsystem and returns to parametric (i.e., Bézier, rational Bézier, B-spline and NURBS) surfaces.
   • Define Your Editor allows you to specify a favorite text editor to be used for typing in the equation of an implicit surface. Selecting this item will cause a dialog box to appear as follows:
     

     This allows you to type in the name of an editor so that when you select Define Implicit Surface your favorite editor will be used. If you do not specify your editor, the default editor is vi. Note that the selected editor must be accessible from your current directory.